1. Field of the Invention
The present invention relates to a load driving apparatus, and more particularly to a load driving apparatus reducing an electromagnetic interference (EMI).
2. Description of Related Art
Referring to FIG. 1A, FIG. 1A is a schematic view of a driving apparatus in a conventional light-emitting diode. In FIG. 1A, the light-emitting diode LD1 is connected in series between a current source I1 and a supply voltage VDD, while the current source I1 receives a control signal CTRL and determines whether to output a current to control the brightness of the light-emitting diode LD1 or not.
Referring to FIGS. 1A and 1B at the same time, FIG. 1B is a waveform graph of the driving apparatus in the light-emitting diode in FIG. 1A. In FIG. 1B, during dimming duration DIT of the driving apparatus, a waveform of a pulse width modulation signal PWM is used as a time for the control signal CTRL to turn on the current source I1, so a current I passes through the light-emitting diode LD1 and enables the light-emitting diode LD1 to emit light. Also, during non-dimming duration NDIT, the current source I1 is turned off through the control signal CTRL to enable the light-emitting diode LD1 not to emit light. The unit duration of the control signal CTRL is labeled by UT, namely, a reciprocal of a frequency of a dimming clock CK. Thus, an average brightness of the light-emitting diode LD1 can be controlled, as long as a duration ratio between the dimming duration DIT and the non-dimming duration NDIT in the dimming period LT is controlled.
It is apparent from the above description that, in order to increase a dimming order of the light-emitting diode LD1, a frequency of a dimming clock CK or duration of a dimming period LT can be increased. However, in addition to increasing current consumption, higher frequency pulse width modulation signals PWM also generate more severe EMI phenomenon, and if the duration of the dimming period LT is increased, a dimming frequency is reduced; as the dimming frequency is the reciprocal of the dimming period, if the dimming frequency is below 20 kHz, an audible sound is generated. Therefore, both the modes above affect the overall performance of the system.